Many systems use engines to produce power for performing various tasks. Engines often produce power by executing a power cycle that includes introducing fuel and air into a combustion chamber and combusting the fuel with the air in the combustion chamber to produce high-pressure combustion gas that expands in the combustion chamber and drives a working member, such as a piston. In many cases, the power cycle that an engine executes includes releasing the combustion gas from the combustion chamber to accommodate introduction of new fuel and air into the combustion chamber during a subsequent power cycle. Often, the engine releases the combustion gas from the combustion chamber after it has expanded once. Unfortunately, releasing the combustion gas from the combustion chamber this quickly may have undesirable results. For example, releasing combustion gas from the combustion chamber after expanding the combustion gas only once may substantially reduce the temperature and pressure of the combustion gas before hydrocarbon particles in the combustion gas have significant time to regenerate.
U.S. Pat. No. 6,443,108 to Brehob et al. (“the '108 patent”) shows an engine that executes a power cycle that includes retaining combustion gas in a combustion chamber after the combustion gas has expanded once. The power cycle disclosed by the '108 patent includes an intake stroke wherein an intake valve is open as a piston of the engine moves in a direction that increases the volume of the combustion chamber so that air fills the combustion chamber. Subsequently, the engine closes the intake valve and holds an exhaust valve closed so that the combustion chamber is closed while the piston compresses the air during a compression stroke. With the intake valve and exhaust valve still closed, the engine of the '108 patent then combusts fuel in the combustion chamber, producing combustion gas that drives the piston through a first expansion stroke.
The engine then holds the intake and exhaust valve closed while the piston compresses the combustion gas in the combustion chamber during a second compression stroke and the combustion gas expands and drives the working member through a second expansion stroke. The '108 patent also discloses that the engine may combust additional fuel in the combustion chamber during the second compression stroke and/or the second expansion stroke. After the second expansion stroke, the engine of the '108 patent opens the exhaust valve so that the piston drives the combustion gas out of the combustion chamber during an exhaust stroke.
Although the engine of the '108 patent executes a power cycle that includes retaining the combustion gas in the combustion chamber after it expands once, certain disadvantages persist. For example, retaining all of the combustion gas in the combustion chamber during the second compression stroke and the second expansion stroke may result in very high temperatures and pressures in the combustion chamber during these phases of operation. This may be especially so because the engine of the '108 patent combusts additional fuel in the combustion chamber during the second compression stroke and/or the second expansion stroke. Very high temperatures and pressures in the combustion chamber during the second compression stroke and the second expansion stroke may create a number of undesirable results, such as high production of NOx and high stress on the components of the engine.
The engine and methods of the present disclosure solve one or more of the problems set forth above.